(1) Field of the Invention
The present invention relates generally to Precision Guided Munitions (PGM), and in particular to a method and a splice for splicing multi-fiber optic micro cables for the guidance thereof.
(2) Description of the Prior Art
Legacy systems used for Precision Guided Munitions (PGM), such as wire guided torpedoes, use thin metal wires to provide a communications link between the munition and the controller. The bandwidth of the communications link decreases linearly with distance, and as the range of these weapons increases, the reduced bandwidth of the interconnecting wire cable limits the rate at which data can be transmitted between a submarine and a torpedo to about 200 baud. Current requirements are for multi gigahortz data rates to enable real time video imaging and on the fly reprogramming. Several initiatives to replace the wire link with fiber optic technology are being pursued. A requirement for using metal wire or fiber optic wire guided torpedoes is that the torpedo's wire must be spliced to the shipboard-side wire. For payout reasons, this splice is more complex when using fiber optics, because the splicing requirements for fiber optic cable must enable continuous light transmission. As will become evident from the discussion below, typically fiber optic wire is spliced incorporating a loop of fiber optic cable to help relieve the stress. A loop is unsuitable for a precision inside payout spool, as it can become entangled in the wraps. Conventional splices, including both mechanical and fusion splices, without the strain relief loop are relatively weak compared to the splice-free cable, and the splice is prone to failure during payout.
FIG. 1 shows a prior art torpedo mounted dispenser (TMD) 10 mounted on an aft portion of a torpedo 12. The TMD 10 is disconnectably attached to the torpedo 12, such that upon launch of the torpedo, the TMD which is fastened in the launch tube, parts from the torpedo 12 and remains in the launch tube. The TMD 10 incorporates a spool 14. A control wire 16 is coiled on spool 14 so as to pay out to torpedo 12 after launch. A fiber optic splice 18 may be needed between TMD 10 and torpedo 12 or between a submarine and an external end of control wire 16.
U.S. Pat. No. 4,043,854 to Georges Le Noane et al. disclose a method for splicing optical fiber cables having an axial core and fibers disposed around the core. At the places where splicing will have to be made, the jacket of the cable is removed, the fibers are glued on the core and two half-shells are disposed around the glued fibers encasing them. The half-shells are bonded to the core and fibers by gluing under pressure. When the glue has set, the half-shells together with the fibers and cable core are sawn perpendicularly to the cable axis which gives two half-shell segments. These segments have registering bores and splicing is achieved by inserting calibrated columns or pins into these bores.
U.S. Pat. No. 4,657,343 to Oldham et al. teaches that when splicing packages containing a number of optical fibers, one cannot guarantee the exact length of each fiber over the joint. Thus the result that some fibers will be shorter than others, and thus there will be some excess length. It is desired to dispose of this excess length in a cavity with the smallest diameter and length possible. The length of the reinstatement tube is preferably such that the optical fibers are arranged in the cavity thereof in a helical snake-like fashion with the minimum bending radius for the fibers not being exceeded.
U.S. Pat. No. 5,050,945 to Sorensen teaches an apparatus and method for splicing light conductors in composite cables, in particular marine cables, comprising a plurality of spliced cable sections of power conductors and sections of light conductors. With a view to uninterrupted armoring along the entire length and thus the ability to maintain a sufficient tensile and flexural strength, the splice of the light conductors is provided at a distance from the splice of the power conductors and with a cross-sectional contour which essentially corresponds to the cable cross-section. Then the armoring is wound uninterruptedly around the cable and encloses the splices of the power conductors as well as the light conductors.
GB2169093 to MacKinlay teaches an optical fiber splice housing for multi-element cables. The invention relates to a protective housing for splices made in optical fibers incorporated in multi-element cables, such as hybrid electric and fiber-optic cables. In a cable comprising one or more optical fibers, it is usual to protect sections of optical fiber containing a splice by preventing tension being applied across the splice and by including one or more loops of optical fiber in the region of the splice within the cable. It is also a common requirement at splice sites in cables containing optical fibers to be able to accommodate a range of surplus lengths of the component optical fibers, which it is convenient to accommodate in the form of loops. All such loops of optical fiber must have a diameter greater than a certain size both in order to prevent optical losses, and to reduce fatigue of the optical fiber due to internal stresses. Limits on the outer diameter of a cable place constraints on the maximum diameter of optical fiber loop that can be accommodated in the cable. In fiber-optic cables and hybrid cables comprising two or more cable elements, there are difficulties accommodating such loops of optical fiber safely and conveniently. For instance, wrapping a length of fiber around the exterior of the cable exposes it to mechanical harm.